Fair Value of Assets and Liabilities - Schedule of Rollforward of Level 3 Assets and Liabilities Held at Fair Value (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Assets
Balance at beginning of period	$ 694	$ 600	$ 676	$ 618
Total gains (losses) included in: Net income	(3)	(5)	4	(2)
Total gains (losses) included in: OCI	(1)	0	1	2
Transfers Into Level 3	0	16	0	16
Transfers Out of Level 3	0	0	0	0
Purchases	35	36	55	78
Sales	(48)	(21)	(57)	(84)
Issues	0	0	0	0
Settlements	(2)	(1)	(4)	(3)
Balance at end of period	$ 675	$ 625	$ 675	$ 625
Net investment income
Total Level 3 gains (losses) included in net income
Fair Value, Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net investment income	Net investment income	Net investment income	Net investment income
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net investment income	Net investment income	Net investment income	Net investment income
Gain (loss) included in earnings	$ 1	$ 3	$ 1	$ (2)
Net gains (losses) on investments and derivatives
Total Level 3 gains (losses) included in net income
Gain (loss) included in earnings	$ (5)	$ 0	$ 0	$ (1)
Operating costs and expenses
Total Level 3 gains (losses) included in net income
Fair Value, Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Operating costs and expenses	Operating costs and expenses	Operating costs and expenses	Operating costs and expenses
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Operating costs and expenses	Operating costs and expenses	Operating costs and expenses	Operating costs and expenses
Gain (loss) included in earnings	$ 1	$ (8)	$ 3	$ 1
Municipal
Assets
Balance at beginning of period	8	17	11	21
Total gains (losses) included in: Net income	0	3	0	3
Total gains (losses) included in: OCI	0	(1)	0	(1)
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Purchases	0	0	0	0
Sales	(1)	(6)	(2)	(9)
Issues	0	0	0	0
Settlements	0	(1)	(2)	(2)
Balance at end of period	7	12	7	12
Corporate - public
Assets
Balance at beginning of period	23	29	26	69
Total gains (losses) included in: Net income	1	0	1	(1)
Total gains (losses) included in: OCI	(1)	0	1	2
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Purchases	11	0	11	0
Sales	(4)	(3)	(9)	(44)
Issues	0	0	0	0
Settlements	0	0	0	0
Balance at end of period	30	26	30	26
Corporate - privately placed
Assets
Balance at beginning of period	54	49	58	55
Total gains (losses) included in: Net income	(2)	(7)	(6)	(11)
Total gains (losses) included in: OCI	0	1	0	1
Transfers Into Level 3	0	16	0	16
Transfers Out of Level 3	0	0	0	0
Purchases	0	1	0	1
Sales	(2)	0	(2)	(2)
Issues	0	0	0	0
Settlements	0	0	0	0
Balance at end of period	50	60	50	60
ABS
Assets
Balance at beginning of period	58	27	58	28
Total gains (losses) included in: Net income	0	0	0	0
Total gains (losses) included in: OCI	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Purchases	14	7	14	7
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	(1)	0	(1)	(1)
Balance at end of period	71	34	71	34
Fixed income securities
Assets
Balance at beginning of period	143	122	153	173
Total gains (losses) included in: Net income	(1)	(4)	(5)	(9)
Total gains (losses) included in: OCI	(1)	0	1	2
Transfers Into Level 3	0	16	0	16
Transfers Out of Level 3	0	0	0	0
Purchases	25	8	25	8
Sales	(7)	(9)	(13)	(55)
Issues	0	0	0	0
Settlements	(1)	(1)	(3)	(3)
Balance at end of period	158	132	158	132
Equity securities
Assets
Balance at beginning of period	408	358	402	333
Total gains (losses) included in: Net income	(3)	7	6	7
Total gains (losses) included in: OCI	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Purchases	9	28	9	70
Sales	(21)	(12)	(24)	(29)
Issues	0	0	0	0
Settlements	0	0	0	0
Balance at end of period	393	381	393	381
Short-term investments
Assets
Balance at beginning of period	21	6	1	6
Total gains (losses) included in: Net income	0	0	0	0
Total gains (losses) included in: OCI	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Purchases	1	0	21	0
Sales	(20)	0	(20)	0
Issues	0	0	0	0
Settlements	(1)	0	(1)	0
Balance at end of period	1	6	1	6
Other investments
Assets
Balance at beginning of period	2	2	2	3
Total gains (losses) included in: Net income	0	0	0	(1)
Total gains (losses) included in: OCI	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	0	0	0	0
Balance at end of period	2	2	2	2
Other assets
Assets
Balance at beginning of period	120	112	118	103
Total gains (losses) included in: Net income	1	(8)	3	1
Total gains (losses) included in: OCI	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issues	0	0	0	0
Settlements	0	0	0	0
Balance at end of period	$ 121	$ 104	$ 121	$ 104